1. Field of the Invention
The present invention relates generally to a drill bit cutting element and method for mounting a cutting element on a drill bit and more particularly to such a cutting element and method in which a new or worn cutting clement is cut to create at least one partial cutting element.
2. Description of the Related Art
A conventional cutting clement for an earth boring drill bit typically comprises a substantially cylindrical backing made from a cemented metal carbide such as tungsten carbide. One end of the backing has a cutting blank, referred to herein as a cutter, bonded thereto. The cutter typically comprises a disk of cemented carbide having a polycrystalline compact diamond (PCD) layer formed on one end thereof which defines a cutting surface. The PCD layer may be of the type having metals leached therefrom to enable the cutting element to withstand higher temperatures. In such cases the PCD layer may comprise a mosaic of smaller PCD elements mounted on the end of the substrate. Such cutting elements are typically mounted on a drill bit body by brazing. The drill bit body is formed with recesses therein for receiving a substantial portion of the cutting element in a manner which presents the PCD layer at an appropriate angle and direction for cutting in accordance with the drill bit design. In such cases, a brazing compound is applied to the surface of the backing and in the recess on the bit body in which the cutting element is received. The cutting elements are installed in their respective recesses in the bit body and heat is applied to each cutting clement via a torch to raise the temperature to a point which is high enough to braze the cutting elements to the bit body but not so high as to damage the PCD layer.
During drilling, the cutting elements are urged against a formation. As drilling proceeds, the cutter and portions of the backing adjacent thereto tend to wear away from one side. By the time wear extends to the middle of the PCD layer, the cutting element is substantially spent and must be removed and replaced or, in some cases, the entire bit must be replaced.
Prior art half cutting elements are usually semicylindrical in shape. In the case of such a cutting element, each half cutting element includes a backing having a substantially flat side surface and a semicircular cross section. A half cutter including a PCD layer is mounted on one end of the backing. While half cutting elements are desirable because they provide all the PCD cutting surface normally used during drilling (with less PCD material), the reduced surface area of the semicylindrical backing provides less surface area for brazing the cutting element to the drill bit body. As a result, half cutting elements are relatively easier than a full cutting element to break away from the bit body. Although prior art high temperature brazes exist which provide high strength bonds, the heat required to effect the bond is high enough to damage the PCD cutting layer. Such brazes cannot be used in the process described above in which a torch is used to braze the cutting elements thereto because the cutters will be damaged.
It would be desirable to provide a half cutting element which could be mounted on a drill bit body as securely as a conventional full cutting element.